An alternative perspective in the literature is that the use of a prior is essential for incorporating knowledge that is available before the experiment begins. This view is advocated in [1]} and [2]}, for example, as well as in the discussion of Examples REF  and REF  above. Taking this viewpoint, many recent papers have formally studied the learning of prior parameters from other available data or across many experiments; see [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}. A recent preprint by [10]} studies combining many prior sources of information in adaptive experiments.
